JPH0572484B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a vibration suppressing device for suppressing vibrations during running in a vehicle construction machine equipped with wheels, such as a wheel loader.

(Prior Art) Conventionally, in vehicle-based construction machinery, as a means to reduce vibrations during running, for example,
As shown in Japanese Patent Application No. 182195, a spring and dump mechanism are provided inside the piston rod of a hydraulic cylinder for extending and retracting the boom of a truck crane, or a boom and arm cylinder of a hydraulic excavator as shown in Japanese Patent Application Laid-open No. 119830/1983. It is known that a buffer cylinder is provided between the arm and the bucket cylinder, or between the arm and the bucket cylinder, separately from the working hydraulic cylinder such as the arm cylinder or the bucket cylinder, but both have a structure. This method is complicated and expensive to manufacture, and has other drawbacks such as a low vibration suppression effect on the vehicle body, making it unsuitable for practical use.

(Object of the Invention) The present invention has been made to solve the above-mentioned conventional problems. It has a high suppressive effect,
Riding comfort is greatly improved and operator fatigue is reduced. Furthermore, there is no risk of the work equipment hitting the vehicle body or the road surface while driving, and the work equipment is held at a stable, predetermined height for safety. The purpose is to provide a vibration suppression device that can be used while driving.

(Structure of the Invention) The present invention provides a vehicle type construction machine in which a working device is supported on a vehicle main body having wheels so as to be able to rise and fall freely via a working hydraulic cylinder, and a vibration suppressing accumulator. A mode switching valve that can be switched between a communicating state and a blocking state to communicate with the load holding side oil chamber of the working hydraulic cylinder, and an oil chamber on the opposite side from the load holding side oil chamber of the working hydraulic cylinder. a vent circuit connected thereto, and a vent switching valve in which the vent is switched between an open state and a closed state in the vent circuit, and in a state where the mode switching valve is switched to a communicating state, the working device is operated. Volume change V _F of the load holding side oil chamber of the above hydraulic cylinder within the range from the reference plane to the required minimum height during running and static holding pressure during running
P _H and the capacity V _A of the above vibration suppression accumulator
and the initial filled gas pressure P _G is P _G · V _A ⁿ ≦ P _H · V _F ⁿ where n is set to be an index due to adiabatic change P _G ≦ P _H.

In this configuration, when the vehicle body vibrates, the working device vibrates in the vertical direction and the hydraulic cylinder supporting this working device expands and contracts.
Here, if the mode switching valve is switched to the communicating state in advance and the vibration suppression accumulator is communicated with the load holding side oil chamber of the hydraulic cylinder, the expansion and contraction movement of the hydraulic cylinder will be absorbed by the spring action of the accumulator and the appropriate Vibration suppression effects are demonstrated and riding comfort is greatly improved. Moreover, because the initial gas pressure _P It reliably prevents you from hitting the road surface, allowing you to drive safely.

Furthermore, if the vent switching valve is switched to the vent open state in advance during the above-mentioned driving, even if the volume of the oil chamber on the opposite side and the oil chamber on the load holding side changes even when the hydraulic cylinder expands and contracts slightly in response to the above-mentioned vibration. Since oil flows smoothly into and out of this oil chamber, the expansion and contraction of the hydraulic cylinder for vibration suppression is prevented from being restricted, and the vibration suppression effect of the accumulator is always properly exerted.

(Example) FIG. 1 shows a wheel loader as an example of a vehicle-based construction machine to which the present invention is applied. This wheel loader has a working device 3 mounted on a front frame 2a of a vehicle body 2 having a plurality of (for example, four) wheels 1. Working device 3
A boom 4 whose base end is rotatably supported on the front frame 2a, a bucket 5 rotatably supported at the tip of the boom 4, an intermediate part of the boom 4, and one side of the bucket 5. a boom cylinder (working hydraulic cylinder) 8 provided between the front frame 2a and the boom 4, and a cross link with the front frame 2a. 6 and a bucket cylinder 9 and the like.

In this wheel loader, the vehicle body 2 may vibrate in response to the undulations of the road surface 30 or during acceleration or deceleration while driving, and in order to suppress this vibration, the following vibration suppression device is installed. There is.

FIG. 2 is a hydraulic circuit diagram of essential parts showing an embodiment of the present invention. In this figure, 10 is a tank, 11
is a hydraulic pump, and a bucket directional control valve 13 and a boom directional control valve 14 are connected to its discharge pipe (hydraulic power source circuit) 12. The head side oil chamber 9a and the rod side oil chamber 9b of the boom cylinder 9 are connected to the boom directional control valve 14 via pipes 16a and 16b. Holding side oil chamber) 8a and rod side oil chamber (load side oil chamber) 8b
is connected.

Between the boom cylinder 8 and its directional control valve 14, a branch pipe 17 is connected in the middle of a load holding side pipe 16a connected to the load holding side oil chamber of the boom cylinder 8, that is, the head side oil chamber 8a. A vibration suppression accumulator 19 is connected to this branch pipe 17 via a mode switching valve 18 so as to be switchable between a cutoff state (work mode) and a communication state (travel mode). A vibration suppressor 20 is thus configured. This vibration suppressor 20 is connected to the boom cylinder 8
between the head side oil chamber 8a and the directional control valve 14,
It is connected by external piping including conduits 16a and 17, and is installed at any position on the front frame 2a within a range that does not interfere with the rotation of the boom 4 and the expansion and contraction operations of the boom cylinder 8. In this case, the vibration suppressor 20 may be directly connected to the outer wall of the boom cylinder 8. The above-mentioned accumulator 19 is a bladder type, a piston type,
A diaphragm type accumulator is used.

On the other hand, a load-side pipe line 16b connected to the load-side oil chamber of the boom cylinder 8, that is, the rod-side oil chamber 8b.
, the vent unload valve 21 is connected, and the vent line 22 of the vent unload valve 21 communicates with the tank 10 via the auxiliary switching valve (vent switching valve) 23 (running mode), and the state where it is cut off. (work mode).

An electromagnetic switching valve is used for each of the switching valves 18 and 23, and the switching valves are switched between a shutoff position (work mode) and a communication position (driving mode) in conjunction with each other by a mode switching switch 24 provided in the driver's cab, etc. . In this case, the mode changeover switch 24 is turned on and off in conjunction with the operation of the travel lever (not shown).
However, each switching valve 18, 23 may be switched, or each switching valve 18, 23 may be switched hydraulically. 25 is a power source such as a battery.

Further, 26 is a main relief valve, 27 is a load check valve, 28 is an overload relief valve,
29 is a check valve for preventing cavitation.

In the above wheel loader, during work such as excavation, the mode changeover switch 24 is set to the work mode (OFF), and the mode changeover valve 18 and the auxiliary changeover valve 23 are set to the cutoff position (work mode) shown in the figure.
Keep it in. In this state, when the boom directional control valve 14 is switched, the oil discharged from the pump 11 is supplied to the head side oil chamber 8a or the rod side oil chamber 8b of the boom cylinder 8, and the cylinder 8 is extended or contracted, and the boom 4 rotates and the bucket 5 is raised and lowered. Furthermore, when the bucket directional control valve 13 is switched, the oil discharged from the pump 11 is supplied to the rod side oil chamber 9a or the head side oil chamber 9b of the bucket cylinder 9, and the cylinder 9 is extended or shortened.
The bucket bag 5 is rotated via each link member 6, 7. This allows work such as excavation and release of loads to be carried out.

During this excavation, high pressure oil may be introduced into the load holding side oil chamber 8a when the boom cylinder 8 extends or contracts, but if the mode switching valve 18 is switched to the working mode, that is, the cutoff position as described above, The high-pressure oil will not flow into the accumulator 19 side, and there is no possibility that the accumulator 19 will be damaged.

In addition, in this work mode, the auxiliary switching valve 23 is also switched to the illustrated cutoff position, so the vent line 22 of the vent unload valve 21 is cut off, and the oil in the rod side oil chamber 8b of the boom cylinder 8 is vented. Directly to the tank 10 via the unload valve 21
The directional control valve 14
As a result, the supply and discharge of pressure oil to and from the rod-side oil chamber 8b of the boom cylinder 8 is smoothly controlled, and the expansion and contraction of the boom cylinder 8 is appropriately controlled. Thereby, the above-mentioned excavation work etc. can be carried out smoothly.

Next, when traveling, after the bucket 5 is pulled up to a predetermined height, each directional control valve 13, 14 is held at the neutral position shown, and the pipes 15a, 15b for supplying and discharging pressure oil to and from the bucket cylinder 9 are opened. Pipes 16a, 1 for supplying and discharging pressure oil to the boom cylinder 8
6b are blocked, the mode selector switch 24 is switched to the running mode (ON), and the mode selector valve 18 and the auxiliary selector valve 23 are switched to the communication position (drive mode), and the driving force from the engine is applied to the wheels. This wheel loader is made to travel by driving the wheel loader 1.

During this traveling, the vehicle body 2 vibrates according to the undulations of the road surface 30 or when accelerating or decelerating.
As a result, the working device 3 vibrates, the boom 4 supporting the working device 3 rotates in the vertical direction, and the boom cylinder 8 supporting the boom 4 may expand or contract. In such a case, the mode switching valve 18 is switched to the communication position (driving mode) and the head side oil chamber 8a of the boom cylinder 8 is communicated with the accumulator 19, so that the vibration of the vehicle body 2 is Every time the boom cylinder 8 expands or contracts, the oil in the head side oil chamber 8a flows into and out of the accumulator 19 via the mode switching valve 18 etc. The boom cylinder 8 is
The expansion and contraction of is gradually reduced, and the above-mentioned vibration is suppressed.

In addition, during the above-mentioned vibration suppression, the auxiliary switching valve 2
3 is switched to the communication position, and the vent line 22 of the vent unload valve 21 is communicated with the tank 10, so the boom cylinder 8
Even if the volume inside the rod-side oil chamber 8b changes when the rod-side oil chamber 8b slightly expands and contracts, oil smoothly flows into and out of the rod-side oil chamber 8b from the tank 10 via the vent unload valve 21. Therefore, there is no fear that the expansion and contraction of the boom cylinder 8 for suppressing vibrations will be restricted, and the vibration suppressing effect of the accumulator 19 will always be properly exerted even during long-distance travel.

Further, even when the road surface 30 has large undulations and the vehicle main body 2 is subject to large vibrations, the lower surface of the working device 3, that is, the lower surface of the bucket 5, is prevented from colliding with the road surface 30.
It is structured as follows in order to avoid being attacked.

First, when driving, as shown by the solid line in Figure 1,
Based on laws and regulations (safety standards for road transport vehicles), the lower surface of the bucket 5 is maintained at a required minimum height H ₀ or more with the road surface 30 as a reference plane. Here, the position where the bucket 5 is at the required minimum height H ₀ is A, the road surface 30
Assuming that the position where the bucket belt 5 contacts is B and the lowest position where the bucket belt 5 can be mechanically lowered is C, when the bucket belt 5 is held above the A position and the vehicle is traveling, the bucket belt 5
By preventing the bucket from descending from the A position to below the B position, it is possible to prevent the lower surface of the bucket 5 from hitting the road surface 30.

Therefore, in FIG. 3, when the bucket 5 moves from the A position to the B position, the boom cylinder 8
The volume change V _F of the head side oil chamber 8a is determined by the following formula.

V _F = (π/4)D ² (L ₁ -L ₂ )N... D: Inner diameter of head side oil chamber 8a of boom cylinder 8 L ₁ : Length of boom cylinder 8 at position A L ₂ : B Length of the boom cylinder 8 at the position An amount of oil corresponding to the volume change amount V _F flows into and out of the head side oil chamber 8a, and the same amount of oil flows into and out of the accumulator 19 side.

Here, on the accumulator 19 side, the amount of oil flowing into and out of the accumulator 19 when the vibration occurs is the gas volume α inside the accumulator 19.
This gas volume α is determined by the capacity V _A of the accumulator 19 and the initial gas filling pressure P _G ;
It is determined by the static holding pressure P _H of the head side oil chamber 8a of the boom cylinder 8 during traveling, and the relationship between these is as follows.

P _G・V _A 〓=P _H・α〓 …… However, η is a polytropic coefficient, and in this case, η = 1.41 as an adiabatic change.

Therefore, in order to prevent the bucket 5 held at the A position from hitting the road surface 30 due to vertical vibration during traveling, the gas volume α in the accumulator 19 must be equal to or smaller than the head side oil chamber 8a of the boom cylinder 8. It can be said that the amount of change in volume V _F or less is sufficient.

α≦V _F …… From the above formula, P _G・V _A 〓≦P _H・V _F 〓 … is obtained.

Furthermore, in terms of vibration suppression, the initial charged gas pressure P _G of the above-mentioned accumulator 19 is
Since it is better to be smaller than the holding pressure P _H of the head side oil chamber 8a, P _G ≦ P _H .

By selecting the capacity V _A and the initial filled gas pressure P _G of the accumulator 19 based on the above formulas, the phenomenon of the bucket 5 hitting the road surface 30 during driving can be eliminated, and an excellent vibration suppressing effect can be achieved. .

Figure 4 shows the volume change V _F of the boom cylinder head side oil chamber 8a when vibration occurs, V _F1 (1.5)
Accumulator 19 that satisfies the above formula for three types of holding pressures P _H1 , P _H2 , and P _H3 when
The figure shows an example of the combination range of the capacity V _A and the initial filled gas pressure P _G , where the lines indicate the holding pressure P _H1 ,
The lines show the cases of the same P _H2 and the lines show the cases of the same P _H3 .

In FIG. 4, for example, when the holding pressure P _H on the cylinder head side is P _H2 (30 Kg/cm ² ), the shaded area is the area that satisfies the above equation. Therefore, by selecting point A on the line, the capacity V _A of the accumulator 19 is set to V _A1 (1.9), and the initial filled gas pressure P _G
It turns out that it is sufficient to set P _G1 (20Kg/cm ² ). In this case, the accumulator capacity is actually increased within the accumulator 19 as shown in FIG.
V _A1 is in a state where it is compressed to the capacity V _A2 , and in this state, V _A1 - V _A2 corresponds to the volume change amount V _F1 of the boom cylinder head side oil chamber 8a.

Similarly, in Fig. 4, point RO indicates the case where the accumulator capacity is V _A1 and only the filled gas pressure _PG is reduced; in this case, point RO in Fig.
The gas pressure P _G and the above holding pressure P _H2 are balanced at the point, and the accumulator capacity V _A1 − V _A3 of V _F2
is smaller than the volume change V _F1 of the boom cylinder head side oil chamber 8a, which is in the safe direction and satisfies the above equation. In addition,
The same applies when the accumulator capacity V _A is decreased while keeping the filled gas pressure P _G the same.

Other Embodiments In each of the above embodiments, a cavitation prevention check valve is provided in place of the vent unload valve 21, and the rod side oil chamber 8 of the boom cylinder 8 is
In the middle of the load-side conduit 16b connected to the load side conduit 16b, the conduit 16b is configured to be freely switchable between a position where it is directly communicated with the tank 10 and a position where it is cut off by an auxiliary switching valve similar to the auxiliary switching valve 23 described above. You may.

In each of the above-mentioned embodiments, the vibration damping effect is achieved by utilizing the throttling effect due to the pressure loss of the pipes such as the conduit 17 and the mode switching valve 18, but between the mode switching valve 18 and the accumulator 19,
A slow return check valve consisting of a throttle and a check valve may be provided so that the throttle actively exerts a vibration damping effect.

The present invention is applicable not only to the wheel loader of the above embodiment, but also to power shovels, truck cranes, and other vehicle-based construction machines equipped with other working devices.

(Effects of the Invention) As described above, the present invention can exhibit a predetermined vibration suppression effect with a simple configuration in which an accumulator is connected to an existing working hydraulic cylinder via an external piping and a mode switching valve. It is easy to manufacture, costs can be reduced, and the spring constant etc. for vibration suppression can be appropriately and easily set.

Furthermore, by setting the capacity of the accumulator and the initial gas pressure as described above,
By switching the mode selector valve to the driving mode, even if vibrations occur while driving, the work equipment such as the bucket can safely travel without hitting the road surface or the reference surface such as the aircraft body, and the spring action of the accumulator will allow the vehicle body to By absorbing such vibrations, an appropriate vibration suppression effect can be exerted, and riding comfort can be significantly improved. In addition, by switching the mode switching valve to the work mode, even if high pressure oil is introduced into the load holding side oil chamber of the hydraulic cylinder during work, it is possible to prevent the high pressure oil from flowing into the accumulator side. can be protected and improve machine life.

Furthermore, a vent circuit is connected to the oil chamber on the opposite side of the load holding side oil chamber in the hydraulic cylinder, and the vent circuit is provided with a vent switching valve that can switch the vent between an open state and a closed state. By opening the vent with the vent switching valve during the above-mentioned traveling, it is possible to prevent the expansion and contraction of the above-mentioned hydraulic cylinder for suppressing vibration from being restricted, thereby ensuring a good vibration-suppressing effect by the above-mentioned accumulator. There is an effect that can be achieved.

[Brief explanation of the drawing]

Fig. 1 is a side view showing an example of a vehicle type construction machine to which the present invention is applied, Fig. 2 is a hydraulic circuit diagram showing an embodiment of the present invention, and Fig. 3 is a diagram showing changing states of the working device when vibration occurs. FIG. 4 is a schematic diagram showing the relationship between the capacity of the accumulator and the initially filled gas pressure, and FIG. 5 is a diagram showing the relationship between the pressure in the oil chamber on the cylinder load holding side and the flow rate flowing into the accumulator. 1... Wheels, 2... Vehicle body, 3... Working equipment, 4... Boom, 5... Bucket, 8... Boom cylinder (hydraulic cylinder for work), 8a... Head side oil chamber (load holding side oil chamber), 8b...rod side oil chamber (load side oil chamber), 9...bucket cylinder,
11...Hydraulic pump, 12...Discharge pipe line (hydraulic power source circuit), 13...Bucket directional control valve, 14...
...Boom directional control valve, 16a...Load holding side pipe line, 16b...Load side pipe line, 18...Mode switching valve, 19...Accumulator, 20...Vibration suppressor, 21...Vent unload valve , 23...Auxiliary switching valve (vent switching valve).

Claims (1)

[Scope of Claims] 1. A vehicle-based construction machine in which a working device is supported on a vehicle body having wheels so as to be able to rise and fall through a hydraulic cylinder for work, including a vibration suppressing accumulator, this vibration suppressing accumulator, and the above-mentioned work. a mode switching valve that can be switched between a communication state and a cutoff state to communicate with the load holding side oil chamber of the working hydraulic cylinder; a vent circuit, and a vent switching valve in which the vent is switched between an open state and a closed state, and when the mode switching valve is switched to the communicating state, the reference surface of the working device is Volume change amount V _F of the load holding side oil chamber of the hydraulic cylinder, static holding pressure P _H during traveling, capacity V _A of the vibration suppressing accumulator, and It is characterized in that the relationship with the initial filled gas pressure P _G is set so that P _G・V _A ⁿ ≦P _H・V _F ⁿ , where n is an index due to adiabatic change P _G ≦P _H Vibration suppression device for vehicle-based construction machinery.